I began with the plan that I’d finish a math course and a nanoelectronics course by Supriya Datta. The math course was a requirement, but the nanoelectronics course was something I really had to do. I had heard stories about what a wonderful teacher Professor Dutta is. For those who do not know it, Supriyo Dutta is the Father of Spintronics – the person who laid down the theoretical foundation of spin devices. I took the course and was hooked from the beginning to the end. Even though we did not have a solid background in quantum mechanics, Prof. Dutta navigated us through the treacherous currents of quantum mechanics, density functional theories, and vector algebra, and taught us the intricacies of spin transport. The quizzes were more like a formality, easy to solve if you had practiced the past papers. He designed the course to give students the necessary intuition to solve electron transport problems on their own.

I highly recommend this course to students with interest in Nanoelectronics.

The MA511 course, unfortunately, was very disappointing. The lecturer, instead of showing us the applications of linear algebra in real problems, just went on copying math notes from a notebook on to the screen. We completed the first few homeworks on time, but eventually lost interest and dropped the course.

Won the SVC Foundation Scholarship

Our group specializes in discovering and investigating the plasmonic properties of new materials – transition metal nitrides and transparent conducting oxides being a few of them. To develop films with excellent optical properties we possess our very own sputtering system. As a lot of my seniors from our group recently graduated, my colleague Deesha and I got the duty of taking care of the system. As titanium nitride is always in high demand from a lot of our collaborators, the system is always hot in demand and needs to be well maintained at all times. Being the superuser is a tough job. We have to provide samples-on-demand to our fellow labmates and our collaborators, ensure the consistency of the sputtered films, make sure that the machine is operational, and develop and optimize recipes for new materials. It’s a demanding job, but also rewarding. For instance, my close association with the sputtering system landed me the SVC-foundation scholarship, that partially covers books and tuition for a year, and pays for conference travel to any conference related to vacuum technology.

I had signed up for the discovery park ambassador program earlier this year. As part of the program, the Ambassadors give tours to visiting faculty and members of the public of the facilities we have here in Discovery Park. As a Birck ambassador, I gave tours of the Birck Nanotechnology Center, which houses the Scifres Nanofabrication Center. It was a really enriching experience. My audience varied from fifth-graders to full professors; so even though I was covering the same material, I had to tune down or expand my descriptions of the cleanrooms and the facilities to suit the knowledge of the audience. And the visitors never ceased to surprise me. For instance, during one of the tours, I was trying to figure out the best way to explain plasmonic tweezers to a work at home mom. The best I could come up with was, “So… when you focus light into a very narrow region, the spot begins to suck in smalls particles and hold them in position.” I didn’t get to the part where plasmonic antennae push the trapping dimensions to the sub-wavelength level. To my surprise, she responded, “Yes, so the dipole force due to the field gradient is what holds it in place. Now the plasmonic antennae enable a high field confinement, and you can trap them in a smaller space, yes?” It turned out that her husband did his PhD in optical trapping.

The following pictures are of a demo of LCDs I was giving to elementary school kids.

Nanodays 2017

Nanodays is a big annual event where all the research facilities open their doors to the public. It’s a three-day long event that features talks by men and women in science, demonstrations of science projects, and x. Representing OSA and SPIE, Deesha, Oksana, Shaimaa, and I manned a table with an assortment

of toys designed to teach people about optical phenomena. The audience this time varied from two to sixty-year-olds. I discovered that I really like explaining elementary science to students. The highlight of the day was when a cute little three year old stole a slinkie from the demonstration set from right under my friend Deesha’s nose.

Became president of the SPIE elections.

Last, but not least, both Deesha and I were nominated for executive committee positions for the OSA and the SPIE respectively, and became the presidents of the respective student chapters.

We look forward to a year full of exciting and enriching events related to optical science.

To get more information about the events and about how to join the groups, comment here, or join the following group.

When I started this blog, I decided that I’d regularly post reviews of interesting papers and articles on a regular basis. Then several things (projects, sub-projects, courses, and qualifying exams to name a few) happened, and this issue had to be put on hold. Now that I have a little time, I’ll attempt to give this a shot.

The first paper I’ll review is on nonlinear optics.

I decided to be thorough and wanted to get a permission from the journal to use the figures and tables on my website, for which, I was asked for a sum of $149 dollars. Hence, the review will be devoid of any figures or tables. This presents a challenge, now, because I’ll have to explain the physics without resorting to graphs, which will be interesting.

So, without further ado, here it is.

The third-order nonlinear optical susceptibility of gold

Authors: Robert W. Boyd, Zhimin Shi, Israel De Leon

Introduction

This is a critique of the paper “The third-order nonlinear optical susceptibility of gold”, by Boyd et. al., published in Optics Communications in 2014. This paper goes over several experimental papers dealing with the nonlinear optics of bulk gold films, points out how largely the measured χ(3) vary with the frequency of the laser used and the pulse duration, and provides a feasible physical explanation for the variance, which has been overlooked in the previous papers. I chose this paper because it is very closely related to part of my Ph.D. work, which involves the characterization of nonlinear optical properties of new plasmonic materials.

Summary of the Paper

The third order nonlinearities of gold can arise mainly from three mechanisms:

The contribution of free electrons

Free electrons do not have a strong contribution to the nonlinear response of bulk gold in the electric dipole approximation. Since there is no restoring force, there can be no nonlinearities in the restoring force. Also, the ponderomotive nonlinearity of free electrons also plays a negligible role in the case of gold because of strong interband transition. When electrons are confined in a small region, e.g. in a nanosphere, they display a nonlinear response because of quantum size effects. But this effect diminishes as the sample gets larger in size.

Interband transitions

This is the dominant effect in bulk gold and arises from the transitions from the 5d valence band to the 6sp band. This provides for the lowest order contribution to the saturation of the absorption associated with this transition.

where A is an angular factor, T1 and T2 are, respectively, the energy lifetime and the dephasing time for the two-level system describing the interband transition, J(ω) is the joint density of states, and P is a constant associated with the momentum operator between the two states. This is the predominant effect that is used to explain the nonlinear coefficients of bulk gold.

2. The hot-electron contribution

This is the contribution to non-linearity that arises from the excitation of the 5d electrons to the 6sp conduction band through laser excitation. This causes the electrons in the conduction band to heat up. This heating causes the population of energies above the Fermi level to increase and that below the Fermi level to decrease, resulting in a change in the dielectric function of gold, in a largely frequency dependent manner. This is also known as the Fermi Smearing contribution. Typical values of this effect range around 10-16 m2/V2. This has a slower response time because it takes about 500 fs for the electrons to heat up and several picoseconds to relax, after which the effect disappears. This is also highly frequency-dependent (for wavelengths ranging from 300 to 800nm).

Boyd argues that the third effect, namely the effect of hot-carriers excited through laser absorption, is a dominant effect in the cases where the nonlinearity observed was larger than typical values of the χ(3) (10-19 m2/V2).

Ranging from the first reported study of the third order nonlinear responses of gold [1], the authors go through several experiments taking note of the laser power and the pulse duration used in the experiments, and the observed χ(3). For papers which did not have the χ(3) calculated, the authors assumed the real part of the refractive index to be zero and used the formula starting from basic equations of permittivity and refractive index.

It was seen that for experiments where long pulses (tens of picoseconds or higher) of lasers were used, the values of χ(3) obtained were in the order of 10-16 m2/V2. This was seen in the papers of Smith et. al., Xenogiannopolou et. al., and Wang et. al. [2,3,6]. Whereas, when short-duration (lower than 1 ps) pulses were used, the values of χ(3) obtained were in the order of 10-19 m2/V2, several orders of magnitudes smaller. These were seen in the papers of Bloembergen et. al., the van Driel group, and Renger et. al. [1,4,5,7].

For the papers reporting very large nonlinear indices, the effect of hot-electrons has not been used to explain the phenomenon. Boyd and his co-authors propose that hot-carrier induced refractive index change may be causing the large value of χ(3). The hot carrier induced χ(3) is also highly frequency dependent, which is also observed in the experiments conducted by the van Driel group, where with a change in the laser wavelength, the χ(3) changed by a factor of 100.

Critique

This paper covered the origin of the nonlinear optical properties of bulk gold quite comprehensively and provided an explanation for the large discrepancies of the nonlinearities that are seen across publications by different groups. By looking at the results obtained by a large number of groups, they have also noticed a trend in the dependence of the nonlinearity of a gold film with the energy and the pulse duration of the laser used to characterize it. Their explanation for the phenomenon is supported by several experiments cited in the paper.

All that being said, the paper has some drawbacks which I should point out.

Some of the papers cited in the article do not seem to add any useful information to support the authors’ point. For example, the authors mention that the paper by Wang et. al. has an error in the calculation of the nonlinearities. But this does not serve to push forward their own point regarding hot-electron-assisted nonlinearity. The paper by Smith et. al. involved the z-scan measurement of the nonlinear absorption of gold composite media. The χ(3) computed in the paper was (-1+5i) x 10-16 m2/V2. Using the same experimental results, Boyd et. al. calculated the real and imaginary parts of χ(3) = (-9.5+2.3i) x 10-15 m2/V2. There is a large difference between the χ(3) computed by Boyd’s group and Smith’s group although they are based on the same experimental data, but the authors do not make a comment on that.

The authors also do not elaborate on why the sign of the nonlinearity varies between papers.

In conclusion, I believe that a good way to really set the hypothesis regarding hot-electron assisted nonlinearity in gold would be for one group performing an array of experiments on several gold films by varying respectively the pump frequency and the pump width. If the χ(3) is indeed high for longer pulse durations as well as has a largefrequency-dependence, it must have a strong contributing factor from hot-electrons.

Overall, I found the organization of details in this paper to be quite easy to follow, and the background provided was sufficient to give even someone unfamiliar with the topic a clear picture of what was being discussed.

Disclaimer 1: I am responsible for the explanations, interpretations, and opinions presented in the review; these do not reflect the views of my group or my mentors.

Disclaimer 2: I have tried to explain everything to the best of my abilities. Feel free to leave a comment if you think something is unclear or incorrect. I will try to address it as soon as possible.

]]>https://sohamssaha.wordpress.com/2016/12/27/paper-review-the-third-order-nonlinear-optical-susceptibility-of-gold-boyd-et-al/feed/0soham1357gmailcomblog-boyd-optics-communications-paper2016: looking backhttps://sohamssaha.wordpress.com/2016/11/27/2016-in-retrospect/
https://sohamssaha.wordpress.com/2016/11/27/2016-in-retrospect/#respondSun, 27 Nov 2016 06:08:17 +0000http://sohamssaha.wordpress.com/?p=277]]>It has been a while since I had a chance to blog. Between classes, work, and life, it’s really hard to keep the promise I made to myself about writing regularly.

Anyway, here’s what had happened between my last post and now.

The Qualifying Exam aka The Ph.D. Lottery:

This was perhaps the biggest achievements for this year. My friends and I took the Ph.D. qualifying exams – a daunting, haunting, four-hour long exam that determines whether you are qualified to pursue a Ph.D. in Purdue.
Most of us, including myself, passed by a respectable margin.

The Soham Saha Library:

The West Lafayette Public Library was having a fundraising sale last month. You could get a bag of books For just three dollars. I always dreamed of having my own library. And thus, the Soham Saha Library was born.
I have never been an ardent reader of non-fiction and thought this would be a good time to start reading them. I ended up buying about thirty non-fiction books, and am currently reading whenever I have free time.
Some of the notable ones among the books:
– The Nobel Duel, by Nicholas Wade – a true story about the rivalry between two Nobel Laureates in Medicine. This is for inspiration.
– The Idea Factory, by Jon Gertner – It’s about the inception of Bell Labs and the brilliant innovations that took place there. It’s an interesting book on the research dynamics of one of the best Labs the world has ever seen.
– Writing Science: How to write papers that get cited and proposals that get funded, by Joshua Schimel – for obvious reasons.
If you happen to have an office at the Birck Nanotechnology Center and are walking past Room 1238, drop by and take a look. You might find something you like.

Miscellaneous:

Made some new friends, learned how to kickbox, the usual random things I do.

Oh yeah, also, the Presidential election happened. But that is too much for one post.
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Yeah.

]]>https://sohamssaha.wordpress.com/2016/11/27/2016-in-retrospect/feed/0soham1357gmailcomSo, you want to go to grad school?https://sohamssaha.wordpress.com/2016/09/18/so-you-want-to-go-to-grad-school/
https://sohamssaha.wordpress.com/2016/09/18/so-you-want-to-go-to-grad-school/#respondSun, 18 Sep 2016 05:26:50 +0000http://sohamssaha.wordpress.com/?p=251]]>This is a email I composed for my brother and sister a couple of years ago, to give them some tips on applying to grad school. These are things I learned the hard way, and wish someone had told me when I was applying. I think they will be helpful to anyone applying to grad school. So, here goes.

Okay. Here’s the list of things you need to do to get into a good university for higher studies – a no-nonsense guide.

1. Have great undergraduate research experience. It isn’t sufficient to say that you’ve worked under so and so for six months. You have to have documented proof that you worked with them. The best case is a publication in a well reputed journal, which takes months and months of hard work in a (sometimes) seemingly hopeless project, which (sometimes) ends in a miracle.

But the normal case is just the Professor’s recommendation. And trust me, it’s hard to get a good one. A recommendation that starts with something like “In the short period of time I have known X for…”, isn’t likely to get you into a single place. To get a good recommendation, you must do consistent, good work, and do 110% of what your advisor has asked you to do. Remember, the professor has nothing, absolutely NOTHING, to gain by giving you a good recommendation. If he’s not responsive, it’s YOUR job to coax him, to goad him, and to convince him into blessing you with a good recommendation. You have to meet with him regularly. It may be months between your working under him and the time you need the recommendation. He will have tens of other students to associate with in the meantime. So, keep in touch. A good way to do this is to send him New Year Cards, Chinese New Year Cards, Christmas Cards, and everything else you can think about, without annoying him. That way, he’ll remember you when the time comes.

2. Recommendation letters: You’ll usually need three letters of recommendation. So better have at least five people ready. Don’t ask for a recommendation a day before the deadline and expect them to do it for you. You need to regularly check is ALL of them have submitted ALL the recommendations. You don’t have any leverage over them, and their lives will be affected by zero amount if you miss an application. So finish your application well before the deadline.

3. Have a great GPA: The median GPA of accepted students in any of the first tier universities is around 3.80/4.00. That’s the median, which means that half the people have a GPA better than that. A good GPA is no guarantee that it’s going to get you in. But a bad GPA is a red flag. Also, if you want to do research in a particular topic, better have A plusses in all the courses you took in that topic.

I shouldn’t be adding this, because if you don’t know this by now, well… you should know this by now. The secret to a good result is – studying. It’s not finding the subject really interesting. It’s not great teachers. It’s not a profound sense of fulfilment that one gets from being enlightened from a lecture. The lecturers are not there to teach you stuff. They are there to stand and give you slides and tutorials. It’s your job to listen and learn, because someone is paying a LOT of money so that you do just that – study. If you can repeat a subject for a better grade, repeat it. And no matter which university you are in, solving past exam papers always helps. Looking at them at the beginning of the term will at least tell you if the questions have any relation with whatever your lecturer teaches in class.

About research

The same goes for good research. When Edison put in a piece of human hair between two electrodes to see if it glows, and when it filled his room with the horrid stench of burnt hair, do you think he was filled with a sense of bliss? No. But he pulled his ass into the lab the next day, and tried again.

Research is not just finding a great idea in your sleep, and then getting instantly famous. It’s doing the same mundane, trivial thing over and over and over again, until something good happens. It’s also about doing the things faster than others, because a hundred other students are probably doing the same thing day and night to finish it before anyone else.

So if you think that you can’t juggle fun and study, either drop fun and just study, or just quit. A university degree is overrated anyways.

4. Have good GRE scores: A lot of good universities don’t ask for GRE scores. But still, it’s an added bonus. But the word list is much harder than the SAT word list. And this need about a few months of practice.

5. TakeGRE subject tests: If you want to do a PhD in a different subject from your Undergrad, you’ll need to take the relevant subject test. The tests are hard, and need at least 3 months of full time study, unlike the SAT subject tests.

6. Select the right Universities to apply to: This requires a different post entirely.

7. Contact your potential advisor: This also needs elaboration.

So there. Now you have a succinct, yet comprehensive guide to getting into a good school for PhD.

One more thing. Doing each of these things perfectly, gives you about 10% chance of getting accepted. Because there are thousands of students who will apply, hundreds of whom will do everything perfectly.

So better get moving from this minute.

If you have time, here are some great resources that can help you:

1. A timeline for applications. https://blogs.cofc.edu/gradschool/2011/02/21/applying-to-graduate-school/

]]>https://sohamssaha.wordpress.com/2016/09/18/so-you-want-to-go-to-grad-school/feed/0soham1357gmailcomInnovate: Soft Photonics 2016 – The Start Up Challenge – The Endhttps://sohamssaha.wordpress.com/2016/07/02/innovate-soft-photonics-2016-the-start-up-challenge-the-end/
https://sohamssaha.wordpress.com/2016/07/02/innovate-soft-photonics-2016-the-start-up-challenge-the-end/#respondSat, 02 Jul 2016 19:31:24 +0000http://sohamssaha.wordpress.com/?p=234]]>So far, teams had been formed and everyone was supposed to develop and idea for a new technology that we were supposed to pitch in front of a judging panel two weeks later. All our products were supposed to have Kirigami Composites as a backbone.

Our initial idea was to make a kind of glass that would change its crystalline structure in response to a stimulus, controlling the amount of light passing through it. The idea was to use them in car windows to prevent cars from heating up when left in the afternoon sun.

After coming back from the Workshop, we began to interview people to see if there was any existing demand for our product.

Imagine that it’s a hot day, and you have left your car out in the open and went to a class. You come out, open the car door, and a wave of hot air heats you. The plastic bottle you left in the bottle holder has melted in the heat, and the car smells of heated leather. What if we could make windows that would leave the heat out but let light in? If your answer is yes, you are our target.

The same window could also be used in buildings to keep them better insulated by controlling the influx or dissipation of heat. Also, since we were controlling the flow of light through the windows, they could also be used for adjustable privacy windows, that prevent outsiders from seeing through building windows.

We started off by interviewing potential customers for our product. And this is where we hit our first bump. While people were frustrated with cars getting heated up in the sun, there was a solution that was fairly easy to implement. Peoples could leave their windows slightly open to let the heat vape out. Also, we were not very sure how much of the heating was taking place just through the windows, since the entire metal body of the car would start heating up in the sun. Beside that, an initial survey showed that people were not willing to pay more than 10-20 dollars for a product. So changing the glasses in cars was out of the question.

The same went for houses. While real estate developers were interested in getting a new kind of glass that would make their buildings more environment friendly, building owners were not so keen on changing the entire window paneling to same a few bucks on electricity.

Well, what next? We decided that we’d put our efforts into developing a film that would be applied to windows instead. We ran subsequent interviews with homeowners, real estate developers, and car owners. This time, people were more enthusiastic about our product, which would not replace a technology that already exists, but augment it.

Next, we looked up potential competition. We saw that Corning Glass was already selling auto-tinting glass panes for offices and houses to save power. However, this technology has a drawback. It would need someone to completely change all the glassing from the windows.

Polytronix is another company that works with something similar. They make films that change their transparency in response to a current passing through them. But they are active devices and consume power, hence won’t really save power for buildings that use them.

So in the end, the final product was to create a film that could change its transparency by changing its mechanical structure, radiate heat out if needed, and automaticaly decrease the transparency of glass, giving you privacy.

We presented our idea in a skype meeting with a panel of judges, along with other groups.

Competitors:

The Matrix – They presented a technology idea to integrate a pressure sensor at the tip of surgical equipment that would help doctors to get a feel of how much pressure they are applying to a tissue during surgery.

Kiragucci – They proposed colour changing fibers to design tents that could blend into their surroundings.

Four photons – They proposed a high precision optical blood pressure monitor.

Synergy Energy Solutions – They started off with the same idea as us, but went on to focus on controlling the light transmission in greenhouses, using colloidal particles flowing through microfluidic channels.

Finally, the winner was – Synergy Energy Solutions.

Overall, it was a wonderful experience looking at how product development works, and how the idea has to be changed and updated at every step until it finds a potential user. And it was a privilege to see how creative people isolate problems and find solutions to them.

Purpose: To participate in the Innovate Challenge, where we form inter-university groups of three and find the most innovative way to solve a current problem.

The group from Purdue. Two of us are travelling on their own.

6 pm: We reach the Holiday Inn Hotel, and refresh ourselves. There seems to be a problem, and our introduction session is set back by two hours, which gives us time to rest.

Meet and Greet:

9 PM: We meet in the hotel dining room. It turns out that four out of the eight students from the Norfolk State University had missed their connecting flight. The organisers come up with another idea on the fly. Instead of each team having one student from each university, we’ll have members from at least two Universities, to compensate for the missing students.

All the participants.

The next morning is rather hectic.

8-8.30 AM: We have breakfast at the main campus.

9-9.30 AM : Johnathan Fay starts the seminar, introducing us to the Start Up journey – how new technologies and ideas are conceived, develop into products, are customised according to consumer needs, and eventually succeed/get thrown away.

Kirigami composites: A special kind of polymer engineering that makes highly elastic microstructures that can be reshaped and reformed using mechanical stress, voltages, etc.

We are asked to choose one and come up with ideas where we use the technologies to solve problems.

Ideation

9.30-11 AM: The ideation session. We split up into groups. Starting off with the Kirigami composites as a root, we make an idea tree, with branches connecting and spreading out to anything we can associate with the composites.

A lot of unexpected things happen here. Going in to the competition, I thought we were going to propose something in the lines of a research proposal. Something very practical, attainable after a couple of years of effort, with potential for use in the near future. I was thinking in the lines of some kind of flexible lens, or a chromatic filter that would come in handy in a laser lab – something very close to the lines of my research. But once we start brainstorming, any trace of sticking to the area of my research go out the window. We talk about colour changing clothes, remotely powering drones, privacy enhancing windows, and power saving walls, with each idea being more boisterous and amazing than the last one.

Here, we also clarify an obvious question that was bugging many of us from the beginning. If we are to come up with new methods of solving a problem, why are we starting off with a technology? shouldn’t we pick a problem first and then come up with a technology to solve it?

The answer is quite simple. Once we have a technology as a kernel, spreading out ideas from it is easier. We have the flexibility of choosing a problem that can be solved with the resources we have, and sometimes, can come up with different ways of attacking a problem that we had never even thought of initially.

We float around from optical filters used for photonic experiments to microfluidic applications, and from there to adjustable lenses in sunglasses. We finally settle for one project.

The Project: To make auto adjusting window screening technologies.

The idea is to develop windows that can keep light in or out, filtering out particular frequencies while letting in others. One use of it could be to conserve heat in buildings, or to keep cars cool during prolonged exposures in the sun. Nothing’s final yet, but it’s a starting point.

Customer Segment and Value Proposition

11.20-12: We learn about finding the customer, and trying to figure out which of their needs our solution caters to. The idea is to give them something that they ‘absolutely need’, not something that is ‘nice to have’.

More about the innovation process

12-3.15 pm: We move on about Ecosystem Mapping and Customer Discovery. This is where we are supposed to modify and update our initial technology to fit customer needs. We learn about interviewing different kinds of people who will be affected by our products. It’s not only the people who are potential buyers that are affected, and how much they are willing to pay for our product. There are competitors who would be hurt by our product, manufacturers who might not be even interested in changing their assembly line to fit our product assembly, and other product owners whose products might complement, or be hurt by our innovation. Also we learnt about what to ask when interviewing people, and what not to ask.

Storytelling session

3.15-4 PM: We get two demonstrations of previous projects by previous teams. They tell us about the challenges they faced, and the steps they had to take to adapt to consumer needs when launching their products.

Storytelling session.

The Beginning

We finish ahead of time. We have two weeks to work with our project, polish our idea, take twenty interviews and finally, present our project in front of a panel of judges.

Concluding statement: We are all heroes!

Conclusion:

Personally, I had decided to take part in this project to get in touch with the business aspect of things. Yes, I’ll be doing a lot of research and learning a lot of things along the way. Perhaps even come out with a couple of patents. But if I want to market my product, and take it up to consumers, do I really have what it takes to go all the way?

If someone had asked me this question before the workshop, I would probably have given them a handwaving idea about where I was about to go with my innovation. But now, the first thing I have to admit to myself is that I had no idea about how launching a product works in the real world.

It was a short workshop with a lot of information crammed in a few hours. At the end of it, I cannot really say that I know a lot about launching a product, but I can say that I know what I don’t know, and I know whom to seek out, when I am looking for the know-how.

]]>https://sohamssaha.wordpress.com/2016/06/09/innovate-soft-photonics-2016-the-start-up-challenge/feed/0soham1357gmailcom2016-06-02 13.31.14.jpg2016-06-02 23.10.41.jpg2016-06-03 11.14.11.jpg2016-06-03 10.58.57.jpg2016-06-03 13.00.08.jpg2016-06-03 15.55.22.jpgThe Spring 2016 Semesterhttps://sohamssaha.wordpress.com/2016/05/25/the-spring-2016-semester/
https://sohamssaha.wordpress.com/2016/05/25/the-spring-2016-semester/#respondWed, 25 May 2016 06:39:15 +0000http://sohamssaha.wordpress.com/?p=123]]>May 10th Marked the end of my second semester at Purdue. To say the least, it was eventful. But that’s no excuse to not find time for blogging. But here’s the round-up of everything that happened this semester.

Coursework:

I took two courses. The first one was ECE606- Solid State Devices. This is a course that deals with transistor physics. I took it as a refresher course on MOS and BJTs, mostly to prepare for my Qualifying Exam coming up on August. To sum this course up in three words – too much information! We had to cover very elementary Schrodinger’s equations, PN Junction physics, BJTs, MOSFETs, and non idealities associated with the devices. As a result, even though we had to go through a lot of concepts, both old and new, I retained very little. The other course we took was ECE618 – Numerical Electromagnetics. This was more relevant to my field – Fields and Optics. We learned the fundamentals of three types of optical simulations: the finite difference time domain (FDTD) method, the Finite Elements Method (FEM), and the Method of Moments (MOM). I had some experience with FDTD and FEM, but worked mostly with CAD software, where I mostly had to draw a shape and plug in some values and get the software to do my dirty work for me. But this time, we had to come up with our codes from scratch. The problems were tough, but with the help of my amazing teammates, we pulled through.

Grades:

ECE60600 : A

ECE61800 : A+

I also received the hard copy of my Masters Degree from NUS, which kind of marks the end of the Singapore arc of my story.

Research:

I am working on quite a few projects now. They are mostly fabrication based. I’ll update more on them once I figure out how much exactly I can disclose about our research without getting into trouble.

My plan for my first PhD year was to get trained on every type of fabrication equipment that I would possibly have to use during my PhD. I wanted to do this because during my M. Eng. degree in NUS, the labs were not centrally owned, so every time I needed to use a new machine, I had to go through a spiderweb of red-tape, and had to depend a lot of different people to get my processes done. While that helped develop my amazing(!) people skills, I decided that while I am okay with getting help from other people, I am not going to depend on someone.

I thought I was done. But there’s still a lot of characterization equipment I need to train on.

Activities and Clubs:

I joined more clubs than I can keep track of this time. Let me give it a shot.

Lafayette Toastmasters Club: This is to improve my public speaking skills.

SPIE and OSA: The International Society for Optics and Photonics, and the Optical Society of AmericaThese two were a must, owing to the fact that I am specialising in optics.

NSAC: The Nanotechnology Student Advisory Council is an organization of students in Purdue with an interest in Nanotechnology.

HKN: The Eta Kappa Nu honour society. I joined this to meet more people outside of the lab. The recruitment process was intense. Activities included volunteering and outreach work, attending industry talks, getting signatures from professors and active members, to selling coffee. I started off pretty late in the semester, and had only two weeks to finish everything. But all’s well that ends well. I got in.

The Boilerout Volunteering Program. This is a club that organizes activities ranging from ushering in theaters, to collecting cans for Food Finders Food Bank. I joined this club mostly as a means to meet new people. Unfortunately, I haven’t really kept in touch with the people I worked with.

BDSA and PUTS: The Bangladeshi Student’s Association (BDSA), and the Purdue University Tagore Society (PUTS) organized an event together to celebrate the International Mother Language Day. One of my goals on my bucket list was to perform in front of an audience, and I grabbed the opportunity. It was an awesome day.

The Discovery Park Ambassador Program: I’ll write about it in another post.

ECEGSA. The Electrical and Computer Engineering Graduate Student Organization is a club that is in charge of all things that add a little fun to PhD life. I enlisted myself in the organizing committee as the Academic Director.

That pretty much wraps up this semester. With most of my courses done, I am looking forward to doing some interesting research now.

]]>https://sohamssaha.wordpress.com/2016/05/25/the-spring-2016-semester/feed/0soham1357gmailcomWhere Newton’s Third Law doesn’t workhttps://sohamssaha.wordpress.com/2016/02/20/newtons-three-laws-of-motion-a-fun-exercise-part-2/
https://sohamssaha.wordpress.com/2016/02/20/newtons-three-laws-of-motion-a-fun-exercise-part-2/#commentsSat, 20 Feb 2016 07:53:13 +0000http://sohamssaha.wordpress.com/?p=115]]>In the last post, I talked about some of the basics of Newton’s three laws of motion.

Reiterating them.

1. The first law is about a body’s reluctance to change its state of motion – If it’s not acted upon by an external force, a body undergoing uniform motion will moving, and a body at rest will remain at rest.

2. The second law is about how a body reacts to a force – The rate of change of momentum of a body is proportional to the force acting on it.

3. The third law states that for every action, there is an equal and opposite reaction.

Here’s an instance, however, where the third law does not apply.

For this bit, you’ll need a little bit of background in electromagnetism.

A moving charge creates a magnetic field around it. The direction of the field is given by the right hand rule. If the thumb of your right hand points along the velocity of a positive charge, your fingers curl along the direction of the field.

A charge moving in a magnetic field experiences a force that is proportional to the charge of the particle, its velocity, and the magnetic field.

F = qv x B.

The direction of the force experienced by the particle can be given by Fleming’s Left Hand Rule, depicted below. If your forefinger points along the direction of the field a positively charged particle is moving through, and your middle finger in the direction of motion , your thumb points along the direction of the force experienced by the charged particle.

Now look at this figure where two positive charges are moving in directions perpendicular to each other.

The red charged particle (Particle 1) is producing a field B1. The blue particle (Particle 2) is moving through the field upwards. As it does so, it experiences F21, which pushes it to the right side, as shown by the red arrow.

According to Newton’s third law, Particle 1 should also feel a magnetic force F12 to the left, created by Particle 2. However, since the field produced by Particle 2 (B2) is zero at point 1, Particle 1 feels no force acting on it when it is directly underneath Particle 2.

So, F12 = 0.

Newton’s Third Law does not apply.

If you want to dig deeper and understand why momentum is still being conserved in this scenario, you can mull over reference 3. It’s explored there in great detail.

[Note: I am omitting the Coulomb forces the particles are exerting on each other. They are equal and opposite. It’s the magnetic forces that aren’t obeying Newton’s Third Law.]

]]>https://sohamssaha.wordpress.com/2016/02/20/newtons-three-laws-of-motion-a-fun-exercise-part-2/feed/1soham1357gmailcomRight hand ruleFleming's left hand rule2016-02-20 06_54_02Newton’s Three Laws of Motion – A fun exercisehttps://sohamssaha.wordpress.com/2016/02/10/110/
https://sohamssaha.wordpress.com/2016/02/10/110/#respondWed, 10 Feb 2016 19:03:23 +0000http://sohamssaha.wordpress.com/?p=110]]>Let me start with an update on my PhD status. Obvious from the frequency of my blog posts, I have been extremely busy with my projects and coursework. But I am glad to say that, thanks to group mates I can trust and talented lab partners I can rely on when I’m in trouble, things could not have been more productive. And honestly, I don’t mind being under a lot of pressure as long as I am being productive.

Okay, now for the topic of this post. I have been wanting for a long time to write about something that’s very basic in physics – Newton’s Laws.

Before I go into detail, here’s a simple question you can ask your friends. And try to answer it as fast as possible, like, in under ten seconds. Come on, you are a smart guy! You shouldn’t take any more time than that.

While you are asking the question, make sure you contract your arm, and make a throwing motion, providing a visual aid for the innocent victim. If you are lucky, you’ll probably make them give you a wrong answer.

It seems like an easy enough question, but you would be surprised how many get this wrong. Of course, the question lacks a lot of detail. Where in space is the object? How far are the nearest bodies that might exert a force on the object?

The object is not going to slow down. Everyone gets this bit right. There’s no air resistance. So nothing slows the ball down. [Unless your time scale is over millennia and the ball loses its momentum bumping into tiny space particles floating around].

Now, why does the ball not speed up? You did exert a force on it that caused it to accelerate, and as I have established before, there’s nothing there to slow it down, right?

Well, it did accelerate as long as your hand was pushing it forward. But as soon as the ball left your hand, it did not have any force pushing on it anymore. So, it would move in a straight line in a constant speed.

But what about the third law? For every action there is an equal and opposite reaction. So if there is a reaction force, why don’t the two forces cancel each other out and the ball remain at rest?

That’s because the action and the reaction force don’t act on the same body. The reaction force exerted by the ball acted on your hand, and decelerated it, as your biceps tied to pull your hand forward. Since the force by the ball was decelerating your hand, it could not cancel out the force your hand was exerting on the ball.

Sweet. So far we’ve covered high school level physics. But honestly, I have seen Olympiad competitors, engineering students, and even PhD students mess up this simple question. Just needs a little misdirection.

Now, after we have kind of established Newton’s laws and their ‘infallibility’, in my next post, I am going to give you an example where Newton’s third law does not seem to work.

]]>https://sohamssaha.wordpress.com/2016/02/10/110/feed/0soham1357gmailcomA reason to pursue science as a careerhttps://sohamssaha.wordpress.com/2016/01/16/a-reason-to-pursue-science-as-a-career/
https://sohamssaha.wordpress.com/2016/01/16/a-reason-to-pursue-science-as-a-career/#respondSat, 16 Jan 2016 17:30:07 +0000http://sohamssaha.wordpress.com/?p=46]]>There is a weird old story in Hindu Mythology.

Indradyumna, the son of Bharat, was the greatest man on Earth. It was well known that there was no one to match his “Dharma-Swabhaav”, his righteousness. As a consequence of his good deeds, he ascended to Swarga (Heaven). There, for thousands of years, he enjoyed the limitless luxuries he earned as a consequence of his good deeds. But one day, Indra, the king of the lesser Gods, told him, “O King, you have done immense number of punyaas (good deeds) in your life and as a result you were here for a very long time. The time on earth past so much that now no one remembers any of your good deeds and hence it is time for you to leave heaven”. [Now, why the God king used such a long convoluted way of saying “Time’s up!” escapes me, but that’s pretty much how dialogues in most religious texts go.]

The rest of the story is about Indradyumna’s quest to find the one creature on the planet that remembered his good deeds.

Note to self: Must find out why a lot of famous Hindu are painted blue.

The crux of the story had always struck me as a kid. That even the deeds of the greatest man on earth are great as long as they are remembered.

There are more several ways to be remembered in history. Becoming a great philanthropist like Mother Teresa. Writing great work of literature like Shakespeare.

But for me, a great way to survive would be to make a scientific discovery.

Nothing underpins the impact of making scientific discoveries more than the story of Archimedes. You know his story about him running in his birthday suit, crying ‘Eureka.’ If you had a good science teacher in your highschool, you might have heard him tell you that it was something about dipping things in water to determine their purity. But you need to delve a little deeper into the story to appreciate the timelessness of an epic scientific figure.

He probably wasn’t bald!

Archimedes died during the siege of Syracuse, during the second Punic War. The name of the war sounds unfamiliar, right? The Punic War took place between the Romans and the Carthaginians. Much like the first and second world wars, the battles saw great strides in scientific discoveries, with all the participants employing cutting edge war machines and military strategy to outclass their opponents. Over a hundred thousand soldiers died in the battles alone, in a war that lasted for seventeen years.

It is one of the battles that shaped human history as we know it. For one thing, if the Carthaginians had won the war, Jesus might not have been born. If you still are not convinced about the epicness of the war, just take a look at the map of the participating nations.

The original “Second World War”

The fact of the matter is, the Second Punic War was at a time, as significant to human histories as the World Wars are to us. However, we barely remember it.

But we remember Archimedes and his naked run in the streets of Syracuse.

So it is not a far off bet to guess that one day, humanity will forget about the First World War, but remember Maxwell and his equations; we’ll forget about Hitler and the Second World War, but remember Albert Einstein’s theories.

And that is a compelling reason to pursue science as a career, for the remote chance that we might find something that lasts through humanity’s history.

Also, the work hours are nice.

Note: The post was inspired from Professor Evgeni Narimanov’s first lecture in his course ECE60400: Electromagnetic Field Theory. This was undoubtedly one of the best classes I have ever taken.